1. Field of the Invention
The present invention relates to a method for producing an objective lens actuator. More particularly, the present invention relates to a method for producing an objective lens actuator having a plurality of elastic support portions.
2. Background of the Invention
An optical pickup apparatus is used to reproduce or record an information signal of, for example, a so-called compact disc (CD) or a magneto-optical disc. The optical pickup apparatus includes a semiconductor laser device used as a light source, an objective lens, an optical system and a photodetector. A light beam emitted from the semiconductor laser device is converged on a recording surface of the optical disc through the optical system by the objective lens. The light beam reflected from the optical disc is separated from the light beam emitted from the semiconductor laser device and is introduced into the photodetector by the optical system. A position of the objective lens in the optical axial direction is adjusted so that the light beam emitted from the semiconductor laser device may track a displacement of the optical disc in a direction perpendicular to a surface of the optical disc, which displacement is generated by a warpage or the like of the optical disc, and the light beam is focused on the recording surface of the optical disc. At the same time, a position of the objective lens in a direction perpendicular to the optical axis of the objective lens is adjusted so that a position of a spot, on the optical disc, of the light beam emitted from the semiconductor laser device may track an eccentricity of the optical disc or a serpentine motion of a track formed on the optical disc. The focus position of the light beam emitted from the semiconductor laser device and the spot position on the recording surface of the optical disc may be performed by adjusting the position of the objective lens in the optical axial direction and the position of the objective lens in the direction perpendicular to the optical axis. An electromagnetic drive type actuator is used for the positional adjustment of the objective lens.
The actuator includes a bobbin on which the objective lens is mounted, a plurality of elastic support members and a drive unit for generating a drive force. The bobbin is supported by the elastic support members so that the position of the objective lens in the optical axis of the objective lens, i.e., the focus position, and the position of the objective lens in the direction perpendicular to the optical axis of the objective lens, i.e., the tracking position may be adjusted relative to the stationary portion. An example of the actuator will be explained with reference to FIG. 1.
In FIG. 1, the actuator 1 includes a lens holder 2, a coil bobbin 3, a plurality of elastic support members 4a, 4b, 4c and 4d, a base 5 and a mount portion 6. An opening to which the coil bobbin 3 is to be mounted and a recess portion to which the objective lens 2a is to be mounted are formed in the lens holder 2. A hole through which the light beam emitted from the semiconductor laser device and the reflected light beam from the recording surface of the optical disc will pass is formed in a bottom of the recess portion. The objective lens 2a is mounted on the recess portion of the lens holder 2 by adhesives or the like. The lens holder 2 is supported to the elastic support members 4a, 4b, 4c and 4d so as to be movable in a focusing direction Fcs and a tracking direction Trk as desired. An opening portion through which a magnetic circuit of the base 5 to be described later is inserted is formed in the coil bobbin 3. At the same time, a focusing coil 3a and a plurality of tracking coils 3b and 3b are provided on the coil bobbin 3. The focusing coil 3a is wound around an axis in parallel with the optical axis of the objective lens 2a. The tracking coils 3b and 3b are each formed by winding coils in an elliptical shape or a rectangular shape and are mounted on one side of the focusing coil 3a. An upper surface of the coil bobbin 3 is covered by a cover 3c. The cover 3c may be formed to have a closed magnetic path as well as a yoke portion to be described later. The coil bobbin 3 is mounted on the opening portion formed in the lens holder 2 with the focusing coil 3a and the tracking coils 3b and 3b being mounted on the coil bobbin 3. The plurality of elastic support members 4a, 4b, 4c and 4d are each formed by elastic members such as leaf springs or the like. The plurality of elastic support members 4a, 4b, 4c and 4d are mounted between the lens holder 2 and the mount portion 6 by adhesives, soldering or the like so as to be in parallel to each other. Mounted on the base 5 are a projection 7 on which the mount portion 6 is mounted, and a pair of yoke portions 8a and 8b which face to each other to form a magnetic circuit. Under the condition that the lens holder 2 and the mount portion 6 are coupled with each other by the plurality of elastic support members 4a, 4b, 4c and 4d, the mount portion 6 is mounted on the projection 7 by adhesives or the like. At this time, the mount portion 6 is mounted on the projection 7 so as not to slant the optical axis of the objective lens 2a. A permanent magnet 9 is mounted on a surface, facing the yoke portion 8a, of the yoke portion 8b. The pair of yoke portions 8a and 8b and the magnet 9 constitute the magnetic circuit. Under the condition that the mount portion 6 is mounted on the projection 7, the focusing coil 3a and the tracking coils 3b and 3b mounted on the coil bottom 3 is inserted into a gap between the magnet 9 and one of the yoke portions 8a. At the same time, the other yoke portion 8b and the magnet 9 are inserted into the opening portion.
In the thus constructed actuator 1, currents are supplied to the focusing coil 3a and the tracking coils 3b and 3b on the basis of a focusing servo signal and a tracking servo signal, respectively. As a result, the lens holer 2, i.e., the objective lens 2a is driven in the focusing direction Fcs and the tracking direction Trk by a DC magnetic field of the magnetic circuit and an alternating magnetic field generated from the focusing coil 3a and the tracking coils 3b and 3b.
In the actuator, upon mounting the elastic support members 4a, 4b, 4c and 4d onto the holder 2, as shown in FIG. 2, the four elastic support members 4a, 4b, 4c and 4d are separated, in advance, apart from an elastic body which forms a the base. A first end of each of the plural separated elastic support members 4a, 4b, 4c and 4d is mounted on an associated one of projections 2b, 2c, 2d and 2e for mounting the lens holder 2 by adhesives, soldering or the like as shown in FIGS. 1 and 2, whereas a second end thereof is mounted on an associated one of projections 6a, 6b, 6c and 6d for mounting the mount portion 6 in the same method.
In addition to the above-described method for mounting the elastic support members 4a, 4b, 4c and 4d, the following method may be considered. Before the plurality of elastic support members 4a, 4b, 4c and 4d are separated away from the plate-like member which forms the base, i.e., under the condition that each of the elastic support members 4a, 4b, 4c and 4d is integral with the member which forms the base, the lens holder 2 and the mount portion 3 are mounted on a predetermined position of the plate-like member. The predetermined position is a position where the lens holder 2 and the mount portion 6 are coupled by the elastic support members 4a, 4b, 4c and 4d as shown in FIG. 1, when each of the elastic support members 4a, 4b, 4c and 4d is separated away from the plate-like member after the lens holder 2 and the mount portion 3 have been mounted. Under this condition, the laser beam is irradiated thereonto, so that each of the elastic support members 4a, 4b, 4c and 4d is cut and separated away from the plate-like member.
However, in order to mount each of the elastic support members 4a, 4b, 4c and 4d onto the lens holder 2 and the mount portion 6 under the condition that each of the elastic support members 4a, 4b, 4c and 4d is separated, in advance, away from the plate-like member which forms the base, the elastic support members 4a, 4b, 4c and 4d must be mounted on the lens holder 2 and the mount portion 6 one by one. For this reason, it is impossible to automate the assembling work, and there would be a fear that the elastic support member would be bent in assembling. The working efficiency is very low, and the parts control would be troublesome. Furthermore, it would be impossible to mount each of the elastic support members 4a, 4b, 4c and 4d onto the lens holder 2 and the mount portion 6 with a parallelism between the elastic support members 4a, 4b, 4c and 4d, resulting in likelihood of generation of twist thereof. If the twist would be generated in the elastic support members 4a, 4b, 4c and 4d, the optical axis of the objective lens 2a would be slanted and the function of the actuator would not be sufficiently exhibited. If the optical axis of the objective lens 2a would be inclined, the light beam outputted from the objective lens 2a would not be correctly incident onto the recording surface of the optical disc, and the reflected light beam from the recording surface of the optical disc could not be introduced into the optical pickup apparatus.
Also, in the above-described method in which the elastic support members are cut by the laser beam after the lens holder 2 and the mount portion 6 have been mounted on the plate-like member in advance, a spark would be generated upon the cutting operation by the laser beam, so that the generated spark would be applied to the elastic support members 4a, 4b, 4c and 4d, the lens holder 2 and the mount portion 6. In the case where the spark would be applied to the elastic support members 4a, 4b, 4c and 4d, a deformation or the like would be generated where the spark is applied. As a result, the displacement of the elastic support members 4a, 4b, 4c and 4d would be prevented in the focusing direction Fcs and the tracking direction Trk and in addition, the focusing servo or the tracking servo would be likely to be offset. In the case where the spark is applied to the lens holder 2, the deformation is generated in the lens holder 2, resulting in difficulty in mounting the objective lens 2a thereon, or in a disadvantage in which the optical axis of the mounted objective lens 2a would be inclined.